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FIGURE 13.6 Drag force of a cable with various surface roughnesses to Reynolds number [6].

reduce the drag force of a cable for a long-span cable-stayed bridge [6]. Referring to the results, the cable with indented surface (C2 and C3) takes a smaller drag force than the cable with uniform roughness (B3). The indented cable was adopted for the cable of Tatara Bridge in Japan, which is the world's longest cable-stayed bridge, and opened to traffic in 1999.

The Strouhal number and the drag force for various structural members are shown in Table 13.1 and Table 13.2 in Section 13.4.

13.2.3 Vicinity Arrangement Effect of Multiple Bluff Bodies [48]

When structures are built or placed in the vicinity area, their wind loads vary through the arrangement of the structures, the distance between structures, and the number of structures. The flow condition varies based on the relative distance between structures and wind load takes various values corresponding to the vicinity arrangement condition.

13.2.3.1 Side by Side Arrangement

The definition of wind load is indicated in Figure 13.7 for a side by side arrangement. In the case of side by side arrangement, since the fluid around a body flows in an asymmetric flow pattern, the lift force is also induced along with the drag force. The wakes of both structures interfere and the lift and drag forces take various values corresponding to the distance between the two structures because of bistable flow running in the gap between both structures. In the following explanations, interval parameter T/D is used. T and D are spacing distance between two structures and representative length, respectively.

Figure 13.8 shows the lift and drag force coefficients of circular structures of side by side arrangement [7]. It is seen that both coefficients take two values against the interval parameter T/D and this fact